1. Field of the Invention
The present invention is related to, for example, a device for measuring performance of a secondary battery, a battery control system and vehicle.
2. Description of the Related Art
A nonaqueous electrolyte secondary battery typified by a lithium ion secondary battery has high energy density and is used as a power source of various mobile electronic devices. Further, in recent years, practical use of the secondary battery is being considered for hybrid vehicles, hybrid two-wheel vehicles, electric vehicles and electric motorcycles. Secondary batteries used for vehicles such as automobiles are required a battery life of 10 to 15 years likewise the automobile itself. Further, when the battery life is ended, it is necessary for the battery to have a minimum of capability to move the vehicle, instead of being unable to function at all. In other words, even at the time of reaching its end of lifetime, a secondary battery should maintain its capacity and be capable of exercising its minimum output.
Meanwhile, when using secondary batteries for vehicles, it is considered indispensable to run diagnostics of the degree of cell deterioration and performance prediction during a long term usage of over ten years. As an indicator for cell output deterioration, an internal resistance of a cell is suitable. If the internal resistance R of the cell is determined, a permissible current value Imax can be calculated. When an open circuit voltage of a cell is expressed as Voc, and a minimum value of usable voltage range is expressed as Vmin, a maximum output Pmax of the cell can be expressed as in the following equation.Pmax=Vmin×Imax=Vmin×(Voc−Vmin)/R 
Since the internal resistance R of the cell can be calculated from the change of cell voltage occurred upon changing the current value, it can be calculated by a resistance measuring device, such as a tester, or from current-voltage data upon cell usage. Further, means for conducting lifetime prediction by obtaining a resistance value of a battery is disclosed in, for example, JP-A 2000-133322 (KOKAI), JP-A 2001-119862 (KOKAI), and JP-A 2004-264076 (KOKAI).
However, since secondary batteries for vehicles are to be used outdoors throughout the four seasons, it should be taken into account that they would be used in a wide range of temperature from 30° C. below zero to as high as 40° C. Particularly, since cell output decreases under low temperature, it is necessary to accurately predict whether or not the batteries have output capacity which is usable for vehicles even under cold conditions. Accordingly, it is important that the method of measuring the state of cell deterioration also includes output characteristics of the cell under low temperature. However, since it is difficult to measure performance by actually obtaining a low temperature state, it was necessary to establish simple means for measuring internal resistance of a cell and predicting temperature change.
Further, in many cases, a particularly large amount of electricity is required when activating a vehicle or equipment. Therefore, the vehicle or equipment may be susceptible to the decrease in cell output under low temperature conditions. Different from the case of output fluctuation during operation, the temperature of a cell upon activation from a halted state is low. Further, a failure in start-up consumes large amount of energy uselessly. Even at present, there are cases in which start-up of vehicles fail in winter due to the decrease in battery output, and causes the battery to run out while repeating the start-up operation. Therefore, a method has been required such that resistance change of a cell caused by temperature is predicted accurately and energy stored in the cell is used effectively for reliable activation.